Effects of high pressure and high temperature on cation ordering in magnesioferrite, MgFe₂O₄, using in situ synchrotron X-ray powder diffraction up to 1430 K and 6 GPa

Disorder in stoichiometric magnesioferrite, MgFe₂O₄, was determined from in situ synchrotron powder X-ray diffraction data [λ = 0.3738(4) Å] at 6, 5, and 3 GPa and temperatures up to 1430 K. The a unit-cell parameter increases linearly on heating at the three different pressures. Higher pressures cause a smaller cell volume, as expected. Cation order was analyzed in terms of the inversion parameter, x, {^iv[Mg_1-xFe_x]^vi [Mg_x/2Fe_1-x/2]₂O₄} and the order parameter Q = 1 - (3/2)x. As pressure increases, the inversion parameter increases in inverse MgFe_2O4 spinel. O'Neill and Navrotsky (1983) and Landau models were used to describe the equilibrium non-convergent ordering process in MgFe₂O₄, and they both fit the data well.